The present invention relates generally to streak cameras and more particularly to a novel streak camera having improved time resolution in the femtosecond time domain.
Streak cameras, which are about fifteen years old in the art, are used primarily to directly measure the time dynamics of luminous events, i.e., to directly time resolve a light signal. A typical streak camera includes a rectangular entrance slit, input relay optics, a streak camera tube including a housing having disposed therein a photocathode, an accelerating mesh, a pair of sweeping electrodes, a microchannel plate, and a phosphor screen, and output relay optics for imaging the streak image formed on the phosphor screen onto an external focal plane. The image at the external focal plane is then either photographed by a conventional still camera or by a video camera.
In use, photons of an incident light pulse pass through the entrance slit and are collected and focused by the input relay optics onto the photocathode of the streak tube to produce emissions of electrons proportional to the intensity of the incident light pulse. The electrons are then accelerated into the streak tube via the accelerating mesh and are electrostatically swept at a known rate over a known distance, thereby converting temporal information into spatial information. These electrons then strike the microchannel plate, which produces electron multiplication through secondary emission. The secondary electrons then impinge upon a phosphor screen to form a streak image. The streak image thus serves as a luminescent "fingerprint" of the time resolved characteristics of the incident light pulse.
An illustrative example of a streak camera is disclosed in U.S. Pat. No. 4,467,189 to Y. Tsuchiya, wherein there is disclosed a framing tube (i.e., streak camera tube) which includes a cylindrical airtight vacuum tube, a shutter plate, and a ramp generator. The container has a photocathode at one end thereof and a fluorescent screen at the other end thereof which is opposite to the photocathode. The shutter plate is disposed between and parallel to the surface of the photocathode and fluorescent screen and has a multiplicity of through holes perforated perpendicular to its surface. The shutter plate also carries at least three electrodes that are disposed perpendicular to the axis of the through holes and spaced parallel to each other. The electrodes divide the surface of the shutter plate into a plurality of sections. The ramp generator is connected to the electrodes. The ramp voltage generated changes in such a manner as to reverse its polarity, producing a time lag between the individual electrode. Developing an electric field across the axis of the through holes in the shutter screen, the ramp voltage controls the passage of the electron beams from the photocathode through the through holes. A framing camera includes the above-described framing tube and an optical system. The optical system includes a semitransparent mirror that breaks up the light from the object under observation into a plurality of light components and a focusing lens disposed in the path through which each of the light components travels. Each of the light components corresponds to each of the sections on the shutter plate. The images of a rapidly changing object are reproduced, at extremely short time intervals, on different parts of the fluorescent screen.
Other U.S. patents relating to streak cameras include U.S. Pat. No. 4,714,825 to Oba; U.S. Pat. No. 4,682,020 to Alfano; U.S. Pat. No. 4,661,694 to Corcoran; U.S. Pat. No. 4,659,921 to Alfano; U.S. Pat. No. 4,645,918 to Tsuchiya et al.; U.S. Pat. No. 4,630,925 to Schiller et al.; U.S. Pat. No. 4,435,727 to Schiller et al.; U.S. Pat. No. 4,413,178 to Mourou et al.; U.S. Pat. No. 4,327,285 to Bradley; U.S. Pat. No. 4,323,811 to Garfield;
Additionally, articles relating to streak cameras include N. H. Schiller et al., "An Ultrafast Streak Camera System: Temporaldisperser and Analyzer," Optical Spectra (June 1980); N. H. Schiller et al., "Picosecond Characteristics of a Spectrograph Measured by a Streak Camera/Video Readout System," Optical Communications, Vol. 35, No. 3, pp. 451-454 (December 1980); and C. W. Robinson et al., "Coupling an Ultraviolet Spectrograph to a Schloma for Three Dimensional Picosecond Fluorescent Measurements," Multichannel Image Detectors, pp. 199-213, ACS Symposium Series 102, American Chemical Society.
Many of the above-described streak cameras have time resolutions in the picosecond range, with some as short as 500 femtoseconds (fs). However, with the now routine generation of laser pulses as short as 30 fs, the detection of luminous events on the 30 fs scale is now important. Accordingly, there is a need for a streak camera whose time resolution is better than existing streak cameras and is preferably in the 30 fs scale.